After saving Carre Island from the beasts you can start to invest in islands to improve tourism (Population, Assets and later on Transport) and trading (Trade, which will affect P. Pumpkin's assortment).

On Tiny Isle you find the Deserted Quarter which you can repeat any time you like. Besides Transport technology, you can also find the ability to research the Ancient Book on a higher level of this area.

Unlocks after defeating Chubking on Metro Isle. Shortly after you free the Desert Isle King, he finds an old map of Sunny Isle, which unlocks new areas on your island. Through gathering the Construction technology you can learn how to recycle and rearrange buildings or plants.

Hidden Cave F is hidden behind a 5-star tree in Secret Base at about level 32.

The "Modern Aircraft" is a piece of Survival Gear, which lets you do your explorations via Kairoman. You can learn how to use the Kairoman to reach Enigma Isle` after investing in it four times (in Hard Mode only).

After having succeeded in all 5 couses, you can level up the cave to level 80 and the coliseum host unfold his true identity: Dr. Mochiporin. This also gives the ability to repeatably research Next-Gen Power. Completing Fortress of Mystery to 100% also gives you the Superalloy Spear, almost the most powerful weapon in the game.